Many industrial processes involve the crystallization or freezing out of a component from a liquid mixture, which is either a solution or a suspension. The component removed from the liquid mixture may be either the liquid phase or solvent, or it may be a dissolved solid which crystallizes or freezes out. When a dissolved solid is crystallized or frozen out by cooling a liquid mixture, this occurs through a reduction in the solubility of the solid in the liquid and removal of heat of fusion. When the liquid is crystallized or frozen out, the cooling must be sufficient to remove enough heat to convert at least part of the liquid to the solidified component.
A specific process in which a component of a liquid mixture is crystallized or frozen out is in the production of fresh water from salt water which, as used herein, includes sea water, brine, and brackish water. In this process, salt water is cooled to a low enough temperature to form ice crystals which are then separated from the salt water, washed, and melted to give fresh water. When the ice crystals form, dissolved salt is excluded from the ice, so that, upon melting, essentially salt free fresh water is obtained. Some U.S. patents which disclose such a process are: U.S. Pat. Nos. 3,012,409; 3,251,192; 3,605,426; 3,367,123; and 4,164,854.
A process similar to that described to produce fresh water is used to concentrate fruit and vegetable juices, particularly orange and grapefruit juices. The juice temperature is lowered until ice crystals form. Continual removal of the ice lowers the water content and concentrates the juice.
One inherent problem with the crystallization or freezing out of a component from a liquid mixture is the following. The component so removed often has a strong affinity to deposit on, or stick to, the surface of a heat exchanger by which the liquid mixture is cooled to separate out the component. Component build up on the heat exchanger surface reduces heat transfer and thereby lowers cooling efficiency. Furthermore, continuation of the build up can result in reduced flow and, finally, plugging of the heat exchanger and/or ancillary equipment and conduits. There is, accordingly, a need for an improved process and apparatus for crystallizing or freezing out a component from a liquid mixture. The improvement should eliminate or at least reduce component build up or deposition on the heat exchange surfaces by which the liquid mixture is cooled.